1. Field of the Invention
The present invention concerns containment structures for storage of nuclear fuel or containment of liquids which are or have been in contact with nuclear fuel and includes ponds and containment structures for the storage of irradiated nuclear fuel elements under water and structures housing nuclear fuel processing plant which, in an emergency, might be required to act to contain liquid discharged from the processing plant.
2. Discussion of Prior Art
Nuclear fuel elements such as those discharged from a nuclear reactor are stored under water in ponds for a period prior to reprocessing in order to allow radioactivity to decay acceptable levels. As the water is radioactive it is essential to avoid leakage resulting in contamination of the ground and the risk of pollution of the water table. For this purpose the concrete floor and walls of the pond can be lined eg with stainless steel sheets. It is important that such a lining is not stressed beyond predetermined allowable limits during both normal operating conditions and extreme hazard conditions. Extreme hazards are considered to be those with a low probability of occurrence (typically 10.sup.-4) generating forces in the lining significantly beyond working conditions, eg earthquakes.
Where dry structures house processing plant secondary containment can be provided by a stainless containment structure having a steel lining. The secondary containment would in the event of a rupture of the primary containment, eg a liquid-containing process pipe or vessel, serve to contain the liquid in a manner similar to containment of liquid in a pond. This secondary lining is therefore required to resist the same extreme hazard conditions which can affect fuel storage ponds.
Various means have been provided in the prior art for resisting such hazards. None has proved entirely satisfactory.